In the course of the manufacture of spherical products, heretofore it has been customary to adopt a method involving a step of holding a plurality of workpieces (raw spherical bodies) by two parallel grinding plates in sandwich style and a step of effecting relative parallel movement of the two grinding plates to cause the workpieces to roll (to grind the entire spherical surfaces) for increasing the degree of sphericity.
In this regard the present applicants have developed a working apparatus which is highly adaptable to machining on workpieces of varying spherical diameters and is capable of performing grinding, super-finishing, and so forth with greater grinding precision, and already filed a patent application as to this apparatus (refer to Japanese Unexamined Patent Publication JP-A 2012-71413). As shown in FIG. 11, in this working apparatus 100, a workpiece (raw spherical body) W is placed on a support 101 constructed of a bearing or the like, and, the workpiece W is held from both sides of it by a pressing roller 102 and a pair of tapered rollers 103 in sandwich style. Then, a cup-type grinding wheel 104 is pressed from above against the workpiece W. The cup-type grinding wheel 104 is driven to rotate about an axis of rotation P perpendicular to the workpiece W-contacted surface (annular contacted part) thereof.
The paired tapered rollers 103 are placed in a uniaxial arrangement, with their smaller-diameter sides opposed to each other, thereby constituting a structure with a V-shaped groove formed at its outer periphery, like a pulley for V-belt. That is, the workpiece W is placed in straddle fashion over the inclined surfaces of the two tapered rollers 103 so as to be retained at its two points. An advantage of this construction is its capacity to handle variations in the spherical diameter of the workpiece W based on the adjustability to the face-to-face distance between the two tapered rollers 103 (the mutual distance in a direction perpendicular to the direction of drilling through the paper sheet with the drawing printed on it).
The paired tapered rollers 103 can be rotatably driven on an individual basis. For example, by rotating the two tapered rollers 103 at the same speed in the same direction, it is possible to allow the workpiece W to rotate regularly about a horizontal axis. On the other hand, with a difference in rotational speed between the two tapered rollers 103, a tilt is imparted to the axis of rotation of the workpiece W. Moreover, by increasing and decreasing the difference in rotational speed between the two tapered rollers 103, it is possible to tilt the axis of rotation of the workpiece W at various angles. Therefore, by continuing such a control to vary the rotational-speed difference, it is possible to impart complex rotary motion to the workpiece W, so that the entire surface (spherical surface) of the workpiece W can pass thoroughly through a location where machining is carried out by the cup-type grinding wheel 104 (contact location). It can thus be said that the two tapered rollers 103 constitute a spheric-rotation driving section 105 for machining (grinding) the entire surface of the workpiece W thoroughly.
In the following specification, the complex rotary motion caused by tilting the axis of rotation of the workpiece W at various angles to perform thorough machining on the entire surface of the workpiece W will be referred to as “spheric rotation”.
In the working apparatus 100, the support 101 serves as an “underside-abutting portion” which supports the workpiece W, and the tapered roller 103 pair serves as a “side-abutting portion” which abuts on the workpiece W to stop its side-to-side movement. That is, the “underside-abutting portion” and the “side-abutting portion” constitute a work setting section 106 for effecting positioning of the workpiece W. Moreover, the pressing roller 102 serves as a “stopper” for retaining the workpiece W to prevent it from being separated from the “side-abutting portion”. It is desirable to add this “stopper” to the construction in the interest of uniqueness and reliability in the positioning of the workpiece W effected by the work setting section 106.
In the working apparatus 100 thusly constructed, when the workpiece W is attached to and detached from the work setting section 106, there is a need to move the cup-type grinding wheel 104 to a retracted position from the machining position. In light of this, for example, a mechanism for moving the cup-type grinding wheel 104 and its rotatably driving section (not shown in the drawings) as well in a direction along the axis of rotation P was adopted (for example, there is known a mechanism for raising and lowering a grinding tool in a vertical direction as disclosed in Japanese Unexamined Patent Publication JP-A 4-135155 (1992).